ACPID event handler for video/brightness(up|down)

video-brightness

#!/bin/sh
set -o errexit

DEVICE=/sys/class/backlight/intel_backlight
BRIGHTNESS_FILE="${DEVICE}/brightness"
MAX_BRIGHTNESS="$(< $DEVICE/max_brightness)"
STEP=$((MAX_BRIGHTNESS / 20))

read_brightness() {
  cat "${BRIGHTNESS_FILE}"
}

write_brightness() {
  local value="${1}"
  if [[ $value -gt $MAX_BRIGHTNESS ]]; then
    value="${MAX_BRIGHTNESS}"
  fi
  echo "setting brightness of ${DEVICE} to ${value}"
  echo "${value}" >"${BRIGHTNESS_FILE}"
}

main() {
  case $1 in
    +) write_brightness $(($(read_brightness) + STEP)) ;;
    -) write_brightness $(($(read_brightness) - STEP)) ;;
  esac
}

main "$@"